Yesterday, I wrote briefly about Cassini’s scheduled flyby of Saturn’s moon, Dione. Today, we are going to take a deeper look at Dione.

Dione was discovered in 1684

Italian astronomer Giovanni Domenico Cassini discovered Dione in 1684. Recognize the name? The first half of the Cassini-Huygens mission is named after Giovanni.

Giovanni Domenico Cassini also discovered three other moons orbiting Saturn: Iapetus, Rhea and Tethys. He also shares credit with Robert Hooke for the discovery of the Great Red Spot on Jupiter in 1665. Cassini described the storm as a “permanent spot.”

Dione is Saturn’s fourth largest moon

Dione’s diameter is measured at 1,122 km (697 miles). This makes it Saturn’s fourth largest moon and the 15th largest moon in the solar system.

Dione’s makeup

Dione’s surface is composed primarily of water ice. Its density is about 1.48 times that of water. That suggests about one-third of Dione is composed of a dense core of rock. But, its mass is just 1.5% of Earth’s moon. Compare that to Titan whose mass is 180% of Earth’s moon.

The wispy streaks of Eurotas Chasmata

wispy streaks ice canyons

35 years ago, NASA’s Voyager mission observed bright, wispy streaks in a region dubbed Eurotas Chasmata. One early theory was that Dione was geologically active shortly after its formation. Cryovolcanism could have resurfaced parts of Dione’s surface creating the bright, wispy streaks.

NASA’s Cassini probe debunked this early theory during its first visits to Dione. The wispy streaks are bright ice canyon walls. Some of the canyons are hundreds of meters deep.

Darker material falls off the sides of the canyon walls exposing bright ice.

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Cassini’s latest flyby

Yesterday, NASA’s Cassini probe flew within 516 kilometers (321 miles) of Dione’s surface. The probe’s cameras and instruments will make additional observations of the Eurotas Chasmata.

The Cassini team is also hoping the probe can detect and determine the makeup of any fine particles coming from Dione. This is an indication of low-level geologic activity.

The latest flyby is a bit different. It’s a targeted encounter and requires a propulsion maneuver to get the Cassini probe on the right trajectory.

Cassini’s mission team expects the first images from yesterday’s flyby to start arriving on Earth as early as this week.

Image credits: NASA

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